1. Field of the Invention
This invention relates to materials and procedures for making low loss connections to optical fibers and optical devices. More particularly, this invention covers the use of thermoplastic polyurethane materials for bridging the gap between the end of one fiber and another fiber, or between a fiber and a device.
2. Description of the Prior Art
The prior optical fiber art teaches various procedures for obtaining low loss connections between lengths of fibers, both between lengths of single fibers and lengths of multiple fiber bundles. One way of doing this is simply to press the ends of the fibers together by means of a connector, for which various designs are known in the art. The ends of the fibers may be first prepared by polishing, or breaking, or slicing, to obtain a more uniform defect-free surface that results in lower loss.
Other means of reducing connection loss are lenses attached to the ends of the fibers, or index matching fluid that fills the gap between the ends of the fibers. This latter technique has the advantage in some cases of reducing the need for preparing the end surface by polishing, or slicing, as the fluid tends to conform to the shape of the end of the fiber. However, fluids such as glycerol tend to trap foreign matter in the gap, particularly while the fibers are being connected, which may increase losses. Furthermore, such fluids are not very suitable when multiple connect/disconnect operations are required.
One technique that avoids many of the problems of index matching fluids is the use of a transparent flexible index matching dome of a material that adheres to the ends of the connectors and bridges the gap between the ends of the fibers; see U.S. Pat. No. 4,107,242, which suggests such materials as silicone rubber. However, improvements in coupling loss and durability of the material bridging the gap are highly desirable.
For connecting an optical fiber cable to an optical device, such as a light emitting diode (LED) or laser source, or a photodiode or phototransistor detector, the prior art generally uses permanent bonding techniques. These typically include the use of epoxy type cements or other thermosetting compounds. It would be desirable in certain circumstances to be able to rapidly connect and disconnect an optical fiber to such an optical device.